Recently multilayer ceramic circuit board have come into use for mounting integrated circuits such as an LSI in order to reduce delay of an electrical signal propagation time.
Conventionally, alumina is generally used as an insulating material for a multilayer ceramic circuit board. However one of the problems of the alumina multilayer ceramic circuit board is that the delay of signal propagation speed is large because the dielectric constant of alumina is as large as about 10 (at 1 MHz). Furthermore, the sintering temperature of alumina is so high as 1,600.degree. C. that a high melting point metal such as tungsten or molybdenum has to be used as the wiring conductor material for the multilayer ceramic circuit board. However, since the electric resistivities of tungsten and molybdenum are comparatively high, these metals cannot be said to be satisfactory as a conductor material suitable for high densification of wiring conductors and speed up of electrical signal propagation speed.
Development of a multilayer ceramic circuit board for a high speed computer using an insulating material having a small dielectric constant is required in order to increase the signal propagation speed and further the multilayer ceramic circuit board is required to have a mechanical strength high enough to withstand the thermal stress produced during the attachment of pins or the like in order to increase reliability.
The use of a metal having a low electric resistivity such as gold, silver and copper is effective for lowering the wiring conductor resistance, but which requires a ceramic insulating material for the multilayer ceramic circuit board to be sintered at a temperature below the melting points of these metals.
In order to increase the electrical signal propagation speed as well as reliability of the multilayer ceramic circuit board, a multilayer ceramic circuit board has been studied and developed which uses an insulating material having a small dielectric constant and a metal material having a lower electric resistivity than tungusten and molybdenum such as gold, silver and copper, as a wiring conductor material.
Japanese Patent Laid-Open No. 11700/1984 or U.S. Patent Application Ser. No. 511,903, filed July 8, 1983 discloses a composite ceramic insulating material for a multilayer ceramic circuit board having a dielectric constant of 4.6-5.2 co-firable with the wiring conductor material such as gold, silver and copper, and consisting of silica and non-crystallized glass essentially consisting of 20-40 wt % of silicon dioxide, 10-20 wt % of aluminum oxide, 5-10 wt % of magnesium oxide and 30-60 wt % of boron oxide. However the mechanical strength of the sintered body formed of the above composite ceramic insulating material is not so high as that of alumina in that 41-53 MPa of flexural strength such that cracks at the sintered body and peeling of metallized layers from the sintered body may be caused due to thermal stress during attachment of pins for input and output to the multilayer ceramic circuit board, which reduces reliability and yield of the resultant product. The reason for the low mechanical strength of the sintered body formed of the above composite ceramic insulating material is considered to be the low mechanical strength of the non-crystallized glass which combines or binds the filler component, silica.
U.S. Pat. No. 4,301,324 discloses a glass-ceramic insulating material for a multilayer ceramic circuit board having a dielectric constant of 5.0-6.5 and a high rupture strength, co-firable with the wiring conductor material such as gold, silver and copper, and consisting solely of a glass ceramic or crystallized glass essentially consisting of 4.2-10 wt % of lithium oxide, 67.8-74.9 wt % of silicon dioxide and 7.5-16 wt % of aluminum oxide. The dielectric constant of the sintered body formed of the above glass ceramic insulating material is comparatively high because of small amount of silicon dioxide contained therein and further a dimensional stability of the sintered body is comparatively low because the sintered body is formed of a sole component, the crystallized glass.